function Merge(pHead1,pHead2){
    if(!pHead1) return pHead2;
    if(!pHead2) return pHead1;
    if(pHead1.val<pHead2.val){
        pHead1.next=Merge(pHead1.next,pHead2);
        return pHead1;
    }else{
        pHead2.next=Merge(pHead2.next,pHead1);
        return pHead2;
    }
}